Threshold Moderation for End-to-End Encrypted Messaging (2023)

Undergraduate: Max Christman

Faculty Advisor: Saba Eskandarian
Department: Computer Science

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Encrypted messaging is used by billions of people daily to ensure private communications. This privacy enables malicious uses, including spam and other abusive or illegal content. Meta’s Messenger service uses a system called message franking to moderate end-to-end encrypted (E2EE) messages. This system gives Meta total authority in moderation decisions as well as full responsibility for moderating many millions of messages a day.

This paper modifies message franking to allow many users to act as moderators, while maintaining the system’s original security properties. The threshold moderation system uses small groups of moderators responsible for each message, who vote on how to act on each report. The protocol uses threshold secret sharing to condition the undeniability of message reports on a majority vote of the moderators. This decentralized protocol prevents the platform from enforcing unpopular moderation policies while alleviating the burden of moderating every message themselves.

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